The Identification and Management of
Radioactively Luminised Aircraft Components
by
Georgette Emma Phillips
URN: 6045466
A dissertation submitted to the Department of Physics,
University of Surrey, in partial fulfilment of the degree of
Master of Science in Radiation and Environmental
Protection
Department of Physics
Faculty of Electronics & Physical sciences
University of Surrey
September 2009
© Georgette Emma Phillips 2009
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Table of Contents:
1. Abstract
2. Introduction
3. Theory
4. Experimental Method for Detection
5. Results
6. Discussion
7. Conclusions and Summary
8. Acknowledgements and References
Annex A: Prior Risk Assessment for Radium Luminised Components
Annex B: Prior Risk Assessment for Tritium Luminised Components
Annex C: Local Rules for Aircraft Components Containing Radioactive Materials
1. Abstract
Industry operating with radioactive materials is legally obliged to manage the
company’s sources under the Radioactive Substance Act 1993(1), and is to ensure staff
safety by adhering to the conditions of the Ionising Radiation Regulations 1999(2). In
order for a company to fully ensure compliance and fulfil their staff safety
obligations, a company must be able to account for their holdings and manage them
appropriately. Only when the holdings are accounted for and their location confirmed,
can a company manage the staff interaction with those radioactive materials.
This Dissertation investigates the issues associated with the identification of
radioactively luminised aircraft components, and the isotopes investigated are tritium
(H3) and radium by comparing the performance of a Mini900 with an EP15 probe,
3
which is of Geiger Muller design, and a Mini900 with a 44b probe, which is a
scintillation probe.
This report will show that for H3, via Bremsstrahlung and in the right conditions, an
EP15 Geiger-Muller tube, which is designed to identify the presence of particulate
radiations, will out perform the 44b scintillation probe, which is specifically designed
to identify the presence of x-rays (the by product of Bremsstrahlung). This report will
also show that both probes could be utilised to identify the presence of radium.
2. Introduction
Aircraft instrumentation has been luminised since the 1920’s so that Aircrew could
fully understand the situation of their, now unsophisticated aircraft, in low lighting
conditions. Instruments were originally luminised by the use of radium being mixed
with a phosphorescent paint and then applied by hand, to the face of each dial. Little
was known about the biological effects of radiation at the time, which meant that few
resources were allocated to radiation safety. After symptoms such as bone growths,
soft tissue growths and tooth loss were identified within in the workforce, an
investigation ensued, confirming that direct interaction with the radium luminised
paint caused ill health to workers.
In the early 1970’s western aircraft instrument manufacturers moved towards the use
of tritium in place of radium, as the process could be automated which greatly reduced
the biological hazards of working with radioactive materials thereby decreasing an
individuals’ radiation dose levels.
4
In more modern aircraft, some instrumentation still requires independent illumination
so that, in the event of an emergency, the pilot and aircrew do not have to solely rely
on the aircraft power to illuminate certain dials and the emergency exits. With this in
mind, instrument manufacturers have now moved on to utilising non radioactive
illumination methods, but companies involved in the use of aging aircraft for test and
evaluation will inevitably come across radium and tritium luminised components and
instrumentation, either in flying the aircraft, aircraft servicing or in the logistical
management of the fleet components.
This report investigates the issues associated with identifying legacy instruments
containing radium and gaseous tritium, by the use of ‘in-situ’ monitoring, and will be
looking into the management systems that would be appropriate for adherence to the
Radioactive Substances Act 1993(1) (RSA93), and the Ionising Radiation Regulations
1999(2) (IRR99).
Radium luminised dials are effectively sealed sources whilst the bezel (glass front)
remains in place and undamaged, however, the radium paint is aging and thereby
‘flaking’, meaning that contamination issues can arise, if the instrument is opened up
for servicing (thereby making the dial an open source). Radium 226 is an
alpha/gamma emitter, decaying to the daughter product of the gaseous Radon 222.
The alpha from the radium is shielded by the bezel for a complete instrument, but
dose assessment should be undertaken for the gamma.
The tritium utilised in aircraft instrumentation is in a gaseous form enveloped within a
glass capsule. Tritium emits a low energy beta that interacts with a phosphorescent
5
paint. The phosphor in the paint is energised by the beta bombardment, thereby
making the instrument detail visible in low lighting levels. Unlike the radium, if an
H3 luminised instrument is broken, the area can be ventilated and the workforce
evacuated to return after the radioactive gas has dissipated (usually one hour). In the
event of a radium luminised instrument breaking, then a Radiation Protection
Supervisor should be on hand, and fully trained, in decontamination and disposal
procedures.
A radiation employer cannot manage any of the above, if they do not understand
where the radioactive holdings are, and which staff interact with them, so a radiation
employer must have a way of identifying which items contain radioactive materials,
and indeed, what radioactive materials are involved.
The experiment within this report may at first glance seem very basic, however, it
investigates a ‘real world’ problem, as the monitoring must be undertaken on aircraft
or in workshops, meaning space is limited and the equipment is be hand held. Also
airworthiness requirements must be considered before moving, altering or placing
signage on any aircraft instrumentation. This experiment utilises two common ‘insitu’ hand held contamination monitors, a Mini900 with an EP15 GM probe and a
Mini900 with a 44b scintillation probe, to attempt to identify if radioactive materials
are present, and if so, which isotopes they may be. For radium, one would expect a
distinctly positive result due to the gamma emission, however, tritium is much more
difficult to identify, as the beta is shielded within the glass envelope, this means that
monitoring must be undertaken in such a way so as to identify the presence of
Bremsstrahlung.
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3. Theory
Management of Radio Nuclides
There are two main pieces of legislation that must be considered before a company
allows radioactive materials on to its non nuclear site. The Radioactive Substances
Act 1993 (RSA93)(1) and the Ionising Radiation Regulations 1999(2) (IRR99).
The RSA93 considers the use, management and disposal of radio nuclides whilst the
IRR99 considers staff interaction and environmental conditions when working with
radioactive materials, and is a regulation under the Health and Safety at Work Act
1974.
Radioactive Substances Act 1993
Under the RSA93(1) most radio nuclides require a Registration from the Environment
Agency (EA) to allow the company to hold and manage those radio nuclides
identified within the Registration application, however, there are some exemptions
under the RSA93 and tritium in a Gaseous Tritium Light Device (GTLD) can be held
under the Statutory Instrument 1985 No.1047 The Radioactive Substances (Gaseous
Tritium Light Devices) Exemption Order 1985(3) – as long as the Exemption Orders’
conditions are met.
Ionising Radiation Regulations 1999
Under the IRR99 Approved Code of Practice (ACOP)(2), Radiation Employers are
required to consider provision of a Radiation Protection Advisor, provision of
Radiation Protection Supervisors, engineering controls, written procedures, area
designation, monitoring requirements, staff engagement and awareness, training and
Personal Protective Equipment (PPE) – all of which is geared towards keeping the
potential dose to a worker As Low As Reasonably Practicable (ALARP) (2).
7
Radium 226
Radium 226 has a half life of 1600 years and has an interesting daughter series
(considering to Polonium 210) (4). The example decay series is as follows:
Ra226 – α → Rn222 - α → Po218 - α → Pb214 – β → Bi 214 – β → Po214 – α
→ Pb210 – β → Bi210 – β → Po210.
Where:
Ra: Radium, Rn: Radon, Po: Polonium, Pb: Lead and Bi: Bismuth.
α is the nucleus ejecting 2 p and 2 n; where p = proton n = neutron, thereby reducing
the atomic number by two and the atomic mass by four – hence Ra226 becomes
Rn222.
β is the action n = p + β- + v; where n = neutron, p = proton, β- = beta and v =
neutrino. Meaning that the atomic number reduces by one, but the atomic mass
remains the same i.e. Pb210 becomes Bi210.
Usually the travel distance of α at STP is a few centimetres and β- particles a few
meters, however, α has a radiation quality factor of 20 and although can be shielded
by a layer of dead skin, can have a relatively significant biological effect if inhaled,
ingested or injected into soft tissue, so the short travel distance should not distract
from careful decontamination considerations.
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Tritium
Tritium, or H3, is an isotone of hydrogen as it has one proton and two neutrons. The
decay mode is via:
n = p + β- + v
Where n = neutron, p = proton, β- = beta and v = neutrino.
H3 has a half life of approximately 12.33 years and emits 100% β- at and energy of
0.019 MeV. As the energy emission is low, it is not unusual for tritiated instruments
to contain Mega Bequerels (MBq) of radioactivity (where one Bq is one atomic decay
per second).
Usually the travel distance of a β- particle can be meters, however, as the gaseous H3
is contained within a glass capsule and the β- energy is low, the glass capsule tends to
shield the β- emission.
β- has a radiation quality factor of 1 due to its low linear energy transfer and tritium
does not have any radioactive daughter products.
Exposure and Biological Hazards
Radium
As stated earlier, radium is an alpha/gamma emitter. Alpha has a short travel distance
at STP but has the largest radiation quality factor. This quality factor is due to the
alphas’ energy being in the MeV range and its’ energy curve looking something like
Diagram 1.
9
Diagram 1: Example Alpha Energy Curve
α track
Energy MeV
Travel
It can be seen from Diagram 1 that the alpha particle is either travelling with energy in
the MeV range, or it is coming to a sudden stop due to the rapid loss of energy.
Exposure to alpha radiation carries the most risk when the particle interacts with soft
tissue. This may be caused by inhalation directly into the lung tissue, ingestion into
the digestive system, injection, or by absorption through the skin.
The Health Protection Agency has undertaken a number of studies on animals, so as
to ascertain the biological effects of acute and chronic exposure to varying radiations,
and along with cohort studies, have managed to confirm that alpha radiation can cause
single or double strand breakages within the cells deoxyribonucleic acid (DNA)
structure, which is contained within the nucleus of the cell.
DNA is a ladder like structure of sugar phosphate backbone held together by
hydrogen bonds – the ‘rung’ of the ladder if you like. At each end of one of these
bonds is either (T)hymine, (A)denine, (C)ytosine or (G)uanine – arranged in base
pairs so as to compliment each other. The complimentary base pairing arrangements
confirm the purpose of the cell i.e. whether the cell is a hair cell or liver cell etc.
10
When the complimentary base pairing has been disrupted, the cell can either remain
unaffected, be affected but attempt to recover, or die – depending on whether the
alpha particle has caused a single or double strand breakage within the cells DNA.
Illustration 1: Example of DNA Strand Breakage
For the purposes of this example, alpha would be considered a heavy ion, and it is
therefore the heavy ion track that should be of note in illustration 1. It can be seen that
direct interaction between the alpha and the sugarphosphate backbone has caused a
double strand breakage, meaning that when the DNA unwinds itself for replication,
information will be lost regarding complimentary base pairing – therefore the DNA
may attempt to replicate, but where information is lost, it will assume pairings.
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Illustration 2: Example of Healthy DNA Replication
It can be seen from Illustration 2 that the complimentary base pairing in the healthy
replication process keeps continuity through the daughter strands: T–A, G–C, C-G, AT etc. Where an interaction between alpha and the DNA may have caused a single or
double strand breakage, the cell may choose to pair T with C, G with A and so on,
potentially causing the cell to die or causing the cell to mutate – thereby causing
biological affects in either the individual exposed, or their future offspring.
Tritum
Generally there are few hazards associated with gaseous H3 whilst it is encapsulated
within the glass, however, the following considerations should be made:
Undamaged capsule: under Regulation 27 of the IRR99(2) wipe tests are not usually
considered appropriate where the source contains solely gaseous radioactive
12
materials, however leaching of H3 through the glass can occur and the H3 can ‘plate
out’ onto nearby surfaces. Therefore, it is deemed best practice to wipe test areas
associated with the storage of tritiated components.
Bremsstrahlung (discussed later in this section) does occur but is considered to have a
very low risk of significant dose.
Damaged capsule: the gaseous H3 will escape and there are three potential
opportunities for biological exposure.
Inhalation: Direct inhalation of the gaseous tritium leaking from the broken
instrument, affecting both ground and air crew dependant on where and when the
breakage occurs.
Absorption: Aircraft cockpits and flight decks are confined areas and there is often a
degree of condensation in the air, from the breath of aircrew and via the changes of
temperature within the airframe due to altitude. This condensation increases the
potential for the gaseous H3 to join any available water molecules in the air, thereby
introducing H3 in liquid form which can be absorbed by the body.
Ingestion: As the tritiated condensation settles on the aircraft surfaces and evaporates,
the H3 can become an ingestion issue as there will be a residual contaminated ‘dust’.
This contaminated dust presents a biological hazard to both ground and air crew via
handling the aircraft and then not washing their hands.
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Beta has a radiation quality factor of 1 and can penetrate skin up to 50 microns,
however, if interacting with soft tissue, via ingestion, inhalation or absorption, then as
can be seen in Illustration 1 (via the x-ray track, which also has a radiation quality
factor of 1), the hydrogen bonds between the complimentary base pairings can be
affected. Again causing the cell to either be unaffected, die, or affected but attempting
recovery.
Bremsstrahlung:
Bremsstrahlung was discovered by a German scientist called Nikola Tesla in the late
1800’s. The German word Bremsstrahlung literally means ‘braking radiation’ and can
be explained as the energy transfer from a β- particle slowing rapidly within an atoms
electron cloud, where the energy of the deceleration converts into an x-ray photon
emission.
These x-rays are a secondary radiation whose x-ray energies are limited to those
energies associated with the originating β- radiation and the relative size of the
electron cloud it interacts with. An example of this can be seen in generic β- shielding
choices within industry, for instance: One would expect to see aluminium or Perspex
utilised as the shielding material, due to the low atomic mass, and therefore relatively
small electron clouds for the beta to interact with, however, if a higher atomic mass
materials were used, such as lead, then one would expect to a greater Bremsstrahlung
effect, meaning that the radiation employer may be simply exchanging the beta hazard
for an x-ray hazard.
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Gaseous tritium is a pure β- emitter and, as stated earlier, is enveloped within a glass
capsule. The β- is shielded by the glass but Bremsstrahlung does occur. This means
that when attempting to identify whether H3 is present in an instrument, the surveyor
should consider attempting to identify the presence of x-rays rather than β-.
Diagram 2: Example of Bremsstrahlung
Originating β- Particle
X-ray emission through
Bremsstrahlung
Nucleus
Electron Cloud
Slowed β-
Assessing Dose
It is important to understand potential dose in varying scenarios, so as to ascertain
which engineering and administrative controls would be required to undertake the
activity, whilst keeping doses as low as reasonable practicable (ALARP), as required
under the Ionising Radiation Regulations 1999(2).
Biological exposure, i.e. dose, is dependant on the activity of the source, the length of
time an individual is exposed, organs exposed, radiation weighting factor and the
amount of radionuclide ingested, injected, inhaled or absorbed.
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Exposure can be assessed as follows:
Dose = dose rate x time.
Equivalent Dose: The measure of biological effects in seiverts (Sv), where;
Equivalent Dose (Sv) = *absorbed dose x radiation quality factor
*Absorbed dose is the energy deposited in a medium, measured in Gray (Gy). 1Gy is
equal to 1Joule of energy per kilogram of medium.
Effective Dose: The effects of radiation on each tissue within the body, where;
Effective Dose (Sv) = absorbed dose x radiation quality factor x tissue weighting
factor
The tissue weighting factor is an important consideration as differing body tissues
have different sensitivities to radiation. i.e skin is less sensitive to β- than the lungs,
therefore this equation should be undertaken for each organ and the totals collated for
the total effective dose.
When specifically considering internal dose to H3, one should refer to Annex III of
Directive 96/29/Euratom for the radionuclide specific 50year total committed dose
figures.
General dose limits are set by the Health and Safety Executive (HSE), derived from
information provided by the International Commission of Radiological Protection
(Publication 103), Euratom and the Health Protection Agency. The HSE have deemed
that 20mSv per annum or 100mSv averaged over 5 years, are limits that should not be
exceeded. The effects of an exposure can be deterministic – whereby there is a
threshold at which effects will be realised, or stochastic, whereby risk increases with
dose. See Diagram 3: Dose/Risk Graph for Deterministic and Stochastic Effects.
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Diagram 3: Dose/Risk Graph for Deterministic and Stochastic Effects
Dose
Dose
Risk
Risk
Deterministic Effects
Stochastic Effects
Monitors
For the purpose of this experiment, an EP15 GM Probe and 42a and 44b Scintillation
Probes
will be utilised and compared in their potential to identify the presence of
tritium. A brief description of how they operate is as follows;
Diagram 4: The Geiger Muller Tube (EP15 Probe)
+Ion
-Ion
X,α
β
Pulse sent to
Mini 900
Monitor for
CPS readout
Gas filed tube
Anode +
Mica window
Cathode -
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It can be seen from Diagram 4 that the ionising radiation primarily enters the GM
Tube through the Mica window, although photon radiations can also enter through the
metal walls of the probe.
Once inside the Tube the incident particles, along with the applied voltage, ionise the
gas giving rise to further ionisation via a Townsend Avalanche. As only one
ionisation within the gas can set off an avalanche, a quenching agent, such as argon, is
added to avoid internal related avalanches.
The ions move towards the anode and cathode – with the positive ions moving to the
cathode (negative charge) and the smaller negative ions moving more swiftly towards
the anode (positively charged).
The negative ions collect on the positively charged anode and the two opposing
charges cancel each other out – creating a ‘pulse’. It is the number of ‘pulses’ detected
that creates the Counts per Second (CPS) reading on the monitor.
It is worth noting that the negative ions move more rapidly than the positive ions,
therefore the slow moving positive ions act to attract negative ions at the anode,
effectively making the positive charge around the anode greater than the original
anode itself.
Another consideration for the GM tube is dead-time. This is the time that the counter
is not counting pulses whilst the anode recharges itself, after a pulse.
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The Scintillation detector operates as follows;
Diagram 5: The Scintillation Detector (44b)
Reflector
Dynode (+)
Output
Sensor
Xγ
Photo Cathode (-)
Beryllium
Shield
Amplified Signal
Photo
Multiplier
tube
Scintillant
It can be seen from Diagram 5 that the incident radiation (in this case x ray or gamma,
as alpha and beta are shielded by the beryllium shield) penetrates the light shield and
reacts with the scintillant, giving off small ‘sparkles’ of light into the reflector.
The reflector reflects the light towards the photo cathode which interacts with the light
to produce e-. The e- move up the photo multiplier tube, gaining in multiplication as
the e- interact with each dynode, eventually reaching the output sensor, which then
sends the signal strength to the monitor for the cps readout.
Due to the design, the scintillation probe does not suffer any dead time.
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4. Experimental Method – For Detection
There was no eating, drinking or smoking in the work area and gloves were worn,
where dexterity was not impaired. Each monitoring instruments calibration was
confirmed by its certification and by the pre-use calibration check, using a Sr90 check
source, then five known radioactively luminised aircraft components were selected for
monitoring.
The radium luminised items selected for monitoring were oxygen gauge and
emergency light switch and the tritium luminised items selected for monitoring were a
compass, fuel gauge and emergency exit handle.
A background reading was taken from each probe and then each aircraft instrument
was placed individually on a workbench and was monitored firstly with the EP15 GM
probe at contact to the bezel, and then with the 44b scintillation probe at contact to the
bezel. The results can be seen in Section 5 – Results.
5. Results
The results from the monitoring experiment are shown in Table 1: Results from
Monitoring Experiment.
Table 1: Results from Monitoring Experiment.
Nuclide
Mini 900 with EP15 Probe
(error: +/-30%)
Mini 900 with 44b Probe
(error: +/-30%)
n/a
2cps
20cps
Radium226
1500cps
1600cps
Compass
H3
8cps
20cps
Fuel Gauge
Emergency Light
Switch
Emergency Exit
Handle
H3
6cps
22cps
Radium226
450cps
500cps
H3
7cps
20cps
Background
Oxygen Gauge
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6. Discussion
Experimental Method
The experiment itself was very basic, however, the issue is a realistic one and the
experiment was designed to reflect the issues genuinely faced by radiation employers
working with older aircraft components.
Identification of radioactively luminised instruments is important because if the
radiation employer does not understand that it is holding radioactive materials then
they are not in a position to manage the items or the staff safety, appropriately.
Monitoring usually takes place in-situ and is undertaken with hand held instruments in
a non-laboratory environment, therefore the monitoring equipment available is
limited. Both monitors are available from Thermo Fischer and are used widely within
industry.
The age of the components tested was unknown, as was the age of the luminising
material, and therefore the number of half lives undergone by the H3 could be as
many as three – meaning that the activities could have dropped from MBq to KBq.
This drop in activity would mean less opportunity for Bremsstrahlung to occur,
making the presence of H3 more difficult to detect due to the Bremsstrahlung photon
emission falling close to background.
In other situations a radiation employer may wish to put shielding in place, to reduce
the output of the radium luminised instruments, however, due to airworthiness
21
constraints, additional shielding is not appropriate, therefore staff interaction must be
assessed for dose rate (Sv/hr).
Results
Alpha and beta radiations cannot penetrate the beryllium window of the 44b, therefore
it is a photon monitor, detecting radiation through scintillation. It can be seen from
Table 1: Results from Monitoring Experiment, that the 44b cps did not rise
significantly when the probe was used to monitor the known tritiated components.
The probe may not have detected the low energy x-rays of Bremsstrahlung due to
either:

The low energy x-rays were ‘hidden’ in the probes background detection due
to the probes ‘current’ being detected in place of radiation, thereby raising the
probes apparent background detection;

The 44b may not have registered the Bremsstrahlung x-rays due to its
calibration being set to identify photons at higher energies.
The EP15 probe does register a slight rise in cps when used to monitor for H3. This
could be due to an extremely low background reading and therefore any change in the
environment might be registered.
Even though the EP15 probe is designed to be sensitive to particulate radiations, it has
proven to be sensitive to a large photon energy range and therefore may be capable of
registering the low energy photons given by Bremsstrahlung.
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The radium luminised aircraft instruments gave very positive findings for both
monitors, with the 44b being slightly more sensitive than the EP15. The positive
readings may be from the higher gamma output from the nucleus, emitted as the alpha
particles are ejected and the nucleus then rearranges itself. From experience, the EP15
is known to ‘over read’ gamma so I would have expected the EP15 to have higher
counts per second, however, being a GM probe it does suffer from a dead time of
approximately 1/10th of a second. With the dead time factored in, the corrected
readings would be greater than that of the 44b probe.
The 44b probe may have responded so positively to the radium due to the gamma
being in an energy range of low MeV, which is closer to its calibrated range of high
keV for the original design of x-ray monitoring.
Errors:
It is worth considering that the monitor calibration has the potential to be +/- 30% due
to the instrument calibration service having to calibrate within 10% range (on an
annual basis), and daily checks being acceptable if the instrument operates within
20% of the calibration information.
This means that there is a potential 60% latitude in monitor performance. An
explanation for this allowable latitude could be due to the random nature of ionising
radiation – as the radioactive decay is not a true constant.
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The +/- 30% on calibrated performance is in addition to the dead time experienced by
the GM Probe whilst the anode recharges after the negative ions negate the positive
charge. Dead time can be in the order of 1/10th of a second, every second.
Bremsstrahlung
This event could be easier to find if the H3 has not been through many half lives as
there would be more beta activity to interact with the atomic structure of the glass
capsule.
Particular attention should be paid to Bremsstrahlung when considering shielding
materials for other radio nuclides emitting beta radiation, either directly, or via the
daughter products. Therefore, when considering shielding materials for beta particles,
one should select a material with a low atomic mass – such as Perspex or Aluminium.
Management of Radionuclides
A company must first decide if the use of radio nuclides is justified or if an alternative
is available. In this case the instruments, for airworthiness reasons, are specific to the
aging aircraft and must be managed under the Radioactive Substances Act 1993(1).
Exemption No.1047 Gaseous Tritium Light Devices(3), states that articles falling
within the ‘Class C Article’ (articles which are installed, awaiting installation in (i) a
vessel or aircraft; or (ii) a vehicle or equipment used or intended solely for use by the
armed forces of the Crown) can be held by a company provided that the following
conditions are met. Some of the conditions are as follows:
24

No Class C article awaiting installation is stored on the premises for more than
one month.

Class C articles are marked with the word ‘radioactive’, have the trefoil
symbol, state the activity when received, state the manner in which the article
will be disposed of.

Records of movements are kept for 6 years.

All reasonable practicable steps are taken to prevent loss, damage or theft.

As a result of damage, tritium gas is dispersed by means of ventilation.

Articles are disposed of under Section 4 of the Order.
The above means that companies must put in place management systems and a
supervisor to ensure the Exemption Order conditions are adhered to. Some of these
management systems might be:

Stock rotation and secure storage.

A supervisor being formally delegated to ensure correct signage, and that
muster logs contain the relevant amount of information and are retained for the
correct period.

Awareness is raised regarding the procedure for damage to the article, in order
for staff to ensure sufficient ventilation of the affected area.
Management of radium must be undertaken by specific registration with the
Environment Agency (EA). If the application for registration is accepted, then the EA
will issue a bespoke registration, which is a legal contract between the radiation
25
employer and the EA, outlining the accounting requirements, record keeping and use
of the equipment.
Disposal or radium luminised aircraft equipment can only be undertaken when the EA
has issued an authorisation for the user to accumulate and dispose of radioactive
waste.
Interesting contradictions can arise regarding following the law and ethical behaviour
towards the environment when considering the disposal of radium luminised aircraft
components. The specific activity (activity to weight - Bq/kg) of the item for disposal
must be declared to the radiation waste management company employed for the
disposal, and the company disposing of radioactive materials is ethically obliged to
keep the volume of radioactive waste to a minimum, due to land constraints.
A radium luminised dial is made of many components meaning that the specific
activity for the entire item can be relatively low, however, it is generally only the dial
face, needle and bezel that are affected by the radionuclide, so an argument (if
deemed safe via a Prior Risk Assessment) can be made to reduce the volume of the
item for disposal by removing the unaffected components.
This action would increase the specific activity due to the overall weight of the item
being less, with the activity remaining the same. Therefore, a balance must be struck
between the specific activity requirements of the EA authorisation and the volume of
the item for disposal.
26
Ionising Radiation Regulations 1999
Under the IRR99 Approved Code of Practice (ACOP)(2), Radiation Employers are
required to consider provision of a Radiation Protection Advisor (RPA), provision of
Radiation Protection Supervisors (RPS), engineering controls, written procedures,
area designation, monitoring requirements, staff engagement and awareness, training
and Personal Protective Equipment (PPE) – all of which are geared towards keeping
the potential dose to a worker As Low As Reasonably Practicable (ALARP).
Radiation Protection Advisor (RPA) – IRR99 Regulation 13(2): A competent
individual possessing the specific knowledge and experience to advise a radiation
employer on the observance of the IRR99. This includes PRA content, Local Rule
content, engineering controls, designation of areas, competency of RPS, monitoring
and surveys, record keeping, signage, storage conditions, justification, optimisation
and ALARP dose to staff.
*It should be noted that an RPA advises on the IRR99 only and it is the company’s
responsibility to ensure adherence to the RSA93 or any Exemptions there under.
Radiation Protection Supervisor (RPS) – IRR99 Regulation 17(2): A company shall
designate a number of RPS’s to undertake the safe management of articles containing
radioactive materials, and these RPS’s shall be identified in the Local Rules.
An RPS is to be in a suitable position within the company to influence staff behaviour
and to liaise with senior management.
27
The role of an RPS is to manage and undertake the following:

Correct designation of areas.

Local Rules are up to date, relevant and communicated to the staff.

Dosimetry is available to Classified Workers, via the Approved Dosimetry
Service (ADS), and any dose received is communicated.

Monitors are appropriate and calibrated.

Surveys and wipe tests are undertaken of work and storage areas.

Area designation is appropriate.

Articles are accounted for.

Correct and appropriate signage for both the articles and the working areas.

Know what to do in the event of breakage, loss or theft.

Liaise closely with the RPA, staff and senior management.

Know and understand the work activities at hand.

Be able to provide evidence of competency.
When an RPS is delegated to manage radium and tritium luminised components or
instruments, their main considerations may be:
Engineering controls:
IRR99 Regulations 8&10(2): Engineering controls are the first tier of radiation safety.
Controls must be utilised where reasonably practicable i.e. cost verses risk reduction.
If it is deemed that the cost can be absorbed by the company, and reduces the risk
sufficiently, then engineering controls should be utilised to reduce the potential risk of
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dose to workers. These controls may take the form of additional ventilation, fire
management systems, secure storage, or an equipment upgrade.
When working with gaseous H3, the most important engineering controls are
ventilation in secure storage and fire management systems in work areas and although
most of the instruments containing H3 are over 12.33 years old, and have therefore
expended at least one half life but these instruments can start with MBq of activity, so
consideration must still be given to their content.
When considering the management of radium, the RPS must be confident of any dose
assessments so as to monitor staff interaction time, and must be confident that no
leakage is occurring, by the initiation of wipe tests on the bezel, and must also be
confident of what actions to take in the event of a breakage.
Administrative controls:
General administration controls are in place when a PRA is written, Local Rules are
made available and communicated, signage is on both the item and the store,
monitoring is undertaken and findings logged, muster log kept up to date and
available for the period outlined within the Exemption Order or EA registration, proof
of competency, decontamination procedure and disposal procedures.
Written procedures: A procedure known as the Prior Risk Assessment must be written
before any radionuclide is brought into the workplace. Once the risks are identified in
the PRA and mitigated to an ALARP dose through engineering controls or via
29
administration and training, then the company must ensure Local Rules are available
to all staff working with ionising radiation.
Content for a PRA – IRR99 Regulation 7(2): A PRA is designed to outline the
potential worst case scenario of dose and to identify the daily usual occupational dose
– if all of the engineering controls and administrative controls are in place. The object
is then to go through the thought process of reducing risk by identifying potential
solutions to the scenarios raised. A PRA should consider the following(2):

Nature of Ionising Radiation

Estimated Radiation Dose Rates

Likelihood of Contamination

Results of Previous Dose Assessment and Survey

Advice from Manufacturer/Supplier

Engineering Control Measures and Design Features in Place and Planned

Planned Systems of Work

Estimated Levels of Airborne/Surface Contamination

Effectiveness and Suitability of PPE

Extent of Unrestricted Access to Working Areas

Possible Accident Scenarios

Consequences of Possible Failure of Control Measures

Preventative Action Measures and Consequence Limitation
The PRA can be a lengthy document as the radiation employer and RPA must
consider the impact and risk mitigation for every potential risk scenario identified.
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A full PRA for radium is included in Annex A and a full PRA for Tritium is included
in Annex B, but the main points to note when assessing the risks associated with
articles containing Tritium are:
Areas where a breakage may occur, such as on the aircraft, in transit and in the store,
staff who may be affected, potential maximum dose and controls that may be put in
place to avoid the maximum potential dose.
Content for Local Rules – IRR99 Regulation 17(2): Local Rules are designed to be a
short, working document that all staff must read before undertaking work with
ionising radiation.
Local Rules content should consider each of these points – as a minimum:

Dose investigation level

Contingency arrangements

Name of the RPS

Identification and description of the work area and its classification

Appropriate work instructions
Example Local Rules for working with radium and tritium can be found in Annex C.
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Monitoring requirements – IRR99 Regulation 19(2):
Wipe tests – radium luminised avionics equipment must be wipe tested every 2 years
and a record kept. More consideration must be taken with tritium as due to the
gaseous nature of the H3 in the H3 luminised aircraft equipment, the IRR99 ACOP
paragraph 487 states that wipe tests are not required.
That said H3 is one of the smallest atomic elements and can ‘leach’ out through the
glass capsule containing it and ‘plate out’ on the storage surface areas, with this in
mind, wipe tests of storage areas should be undertaken at least annually and the
storage areas should be well ventilated.
Instruments Surveys and Dosimetry (ADS)
Radiation employers are legally obliged to keep radiological doses to As Low As
Reasonably Practicable (ALARP). With this in mind a Radiation Protection
Supervisor is delegated to undertake Monitoring so as to indicate whether the levels of
radiation and contamination are safe for work with ionising radiation to be undertaken
or continue. All activities are to be undertaken with guidance from the Radiation
Protection Advisor in accordance with the Ionising Radiations Regulations 1999(2).
Should a suspected gaseous H3 exposure occur in the work environment then the staff
member is required to provide a urine sample after 24, 48 and 72 hours. These
samples should then be sent to an Approved Dosimetry Service (ADS) for radio
assay.
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The uptake period for tritium is 48 hours and after this period, if found positive for
exposure, one would expect to see the daily dose figures reduce, due to the
radionuclide leaving the body via urination and defecation. Best practice is for the
staff member to drink as much liquid as possible, so as to ‘flush’ H3 from the body.
Even though the H3 in the samples will reduce over time, tritium can remain in the
body for several months, therefore, samples should continue to be taken at regular
intervals, until the H3 content reaches background.
It is worth noting that gaseous H3 has no associated taste or odour and that the dose
assessments are retrospective.
Staff Awareness:
Accounting – the RPS must be in a position to understand the movement of
equipment from the aircraft to the stores. Any breakdown in communication could
lead to the item being unaccounted for and ergo legally mismanaged, therefore the
RPS must work closely with the engineers to understand the daily logistics of the
item.
The RPS must inform the staff they are working with radionuclides and of what to do
in the event of breakage, loss or theft, and the actions to be taken in the event of a
perceived exposure. This is generally undertaken via the Local Rules.
If the RPS fails to do this, then the staff member will not know which items are
radioactive (as the trefoil is placed on back of aircraft instruments and cannot be seen
on the facia when the instrument is fitted to the aircraft) – this means that potentially
33
no action would be taken in the event of a breakage, and the company could breach
their responsibilities under the RSA93(1) and the IRR99(2).
Pre-Legislation
Illustration 3: Example of Radiation Work before Legislation and Controls:
I raise the pre-legislation photograph shown in Illustration 3, take to bring home the
message that if the radiation employer doesn’t manage its radioactive materials
correctly, then the staff cannot behave appropriately – as they won’t know of the
hazards present.
It is unknown where the picture shown in Illustration 3 was taken, however for the
purpose of this discussion, it is assumed that the image was taken in the United
Kingdom, in the 1950’s.
The ladies shown in the illustration are radium dial painters, employed to administer
the radioactive paint to aircraft dial faces and needles, by hand.
34
Radium was added to the phosphorescent paint and administered by brush, making the
exact quantities on each dial, unquantifiable, due to the amount of paint applied onto
the brush being unknown and individualistic, as well as the amount of paint applied to
each line of the dial being dependent on the painters technique.
It can be seen that there are no engineering controls in place and that there is no
apparent signage. As the inherent dangers of working with radiation were unknown at
the time, it can be assumed that there was little or no staff training or radiation safety
awareness programs. With this in mind, the ladies suffered many biological effects
due to their ‘tipping’ the paintbrush in their mouths, in order to retain a point on the
brush, to paint the fine detail required on the needles and dials.
Dial manufacturers have moved away from using radioactive materials to luminise
aircraft dials, but, if there were a requirement for dials to be radium luminised today,
then it would be reasonable to assume that the Prior Risk Assessment would prove
that the process should be automated, so as to remove any biological interaction with
the isotope.
An automated process would also make radium usage quantifiable, so as to manage
and ascertain the specific activity of the radium paint and the amount of paint
administered to each dial.
The benefits of such a process might be to ensure dose is kept ALARP(2) to the staff
and that the radiation employer would be in a position to fully understand their
35
holdings, in order to adhere to any Environment Agency requirements of the
Exemption Order or Registration.
This information could also be fully utilised if and when the end user of the radium
luminised equipment decides to dispose of the dial, in order to apply and comply with
the terms and conditions of the EA Authorisation to accumulate and dispose of
radioactive materials.
If the radiation employer could realistically argue that the cost of full automation
would not be practicable, then other engineering controls could be employed. These
may include the use of tong boxes, the placement of additional shielding and moving
the work stations further apart. The work stations should be well ventilated (with
airflow moving away from the worker) and easily decontaminated by being made of
non absorbent, smooth surfaces.
With either of the solutions mentioned above, it would be reasonable for the radiation
employer to put in place administrative controls, which will include: Prior Risk
Assessment, Local Rules, staff training and awareness, signage, nomination of a
competent Radiation Protection Advisor and Radiation Protection Supervisor,
sampling procedures for air and surface, dosimetry for the workers, area
classification, monitoring and controlling entry into supervised and controlled areas,
bioassay arrangements for incident scenarios, ensuring maintenance, calibration and
daily checks of contamination monitors. All of which is clearly missing from the
workplace shown in Illustration 3 – because they didn’t understand what they were
working with.
36
In addition to the potential engineering and administrative control solutions
mentioned in the previous paragraphs, it should also be noted that PPE and RPE must
be available to the radiation workers as and when required. It can be clearly seen from
Illustration 1, that neither are present. However the employer should be commended
for providing a foot box to the lady in the left of the photograph – perhaps she had a
back problem.
7. Conclusion and Summary
The use of radioactively luminised aircraft components is a legacy issue that must be
managed by all companies associated with the use, maintenance, calibration and
airworthiness of these aircraft components.
These companies cannot rely on historical records as they are not always available,
therefore a cost effective, practical and robust alternative means of identification
should be available.
This investigation has shown that both the EP15 probe and the 44b probe can be
utilised to identify the presence of radium, and that the presence of radium can be
assumed by the significant counts per second compared to that of the tritium findings.
The surveyor attempting to identify the presence of gaseous H3 in aircraft
instrumentation should be aware that they are monitoring for low energy x-rays (due
to Bremsstrahlung) rather than beta particles. With this in mind, it can be seen from
the results in Section 5, that the EP15 probe has proven the most appropriate probe for
attempting to identify the presence of H3, in a low background environment.
37
Once identified, the correct management of known radioactively luminised
components entails the radiation employer adhering to the Radioactive Substances
Act 1993(1), the GTLD Exemption Order(3), and in complying with the Ionising
Radiation Regulations 1999(2).
The consequences of not identifying these instruments can include; unforeseen staff
exposure to the isotope, corporate negligence under the RSA93(1), legal action on the
company, by the Environment Agency.
8. Acknowledgements and References
Acknowledgements:
I would like to thank QinetiQ for their continued professional support and the
Department of Physics, University of Surrey, for the opportunity to investigate and
discuss the results within this report.
References:
(1) Her Majesty’s Government: The Radioactive Substances Act 1993, Chapter 12,
London, The Stationary Office Limited, 1993 reprinted 1999.
(2) Health and Safety Commission: Working with Ionising Radiation, Ionising
Radiation Regulations 1999 – Approved Code of Practice, London, The Stationary
Office Limited, 2008.
38
(3) Her Majesty’s Government: Statutory Instrument 1985 No.1047; The Radioactive
Substances (Gaseous Tritium Light Devices) Exemption Order 1985, London, The
Stationary Office Limited, 1987.
(4) D Delacroix, JP Guerre, P Leblanc, C Hickman: Radiation Protection Dosimetry,
Radionuclide and Radiation Protection Data Handbook 2002, Vol.98 No. 1 2002,
Nuclear Technology Publishing, 2002.
39